Producing steel and high-phosphorus slag.



WILLIAIM R. WALKER, OF NEW YORK, N. Y.

PEDIJUCING STEEL AND HIGH-PHOSFHOR-US SLAG.

1,2Q9,Z2, I specification of Letters Patent.

Ho Drawing.

To all whom "it may concern:

Be it lrnown'that I, WIrLiAM R. WALKER, a citizen of the United States, residing in the city, county, and State of New York, have invented certain new and useful Improvements inProducing Steel and High- Phosphorus Slag, of which the following is a specification.

It has heretofore been proposed to manufacture steel and at the same time to secure a slag rich in soluble phosphates for use as a fertilizer. The processes proposed contemplate the refining in an open-hearth or an electric furnace of pig iron containing a high percentage of phosphorus or of a mixture of such pig llOIl with scrap, using a lime slag.

With the iron ore of foreign countries con-- taining a comparatively high content of phosphorus such processes have been found practicable and economical. But most of the ores of this country are low in phosphorus compared with the phosphoric ores of Europe. Consequently, the pig iron from these compartively low phosphorus ores has not contained enough phosphorus to produce a slag rich in phosphates.

According to this invention I propose a method by which the slag will be made richer in phosphates than if the pig iron were converted into steel directly in the opemhearth or electric furnace. This will make it possible to secure a slag commercially available as a fertilizer from comp'aratively low phosphorus'ore or pig iron; and will increase the percentage of soluble phosphates which can be secured in slags from ores or pig of high phosphorus content. The lowest content of soluble phosphate of lime at which the slag is commer-' cially available as a fertilizer 1s about twelve of-thirteen per cent. With comparatively low phosphorus pig iron ,1 have secured a slag running considerablyhigher than this in soluble phosphates.

American pig iron generally contains about 1.25 per cent. of silicon and about .2 per cent. of phosphorus, these percentages being Widely varied. Thev silicon content will vary with. the heat at which the smelting operations are carried on, and the purposes fd'r which the ig iron is to he used. fflhe hosphorus con nt Will vary depending upon the character of the ore used in tfe smelting operation which varies with th district from which it is obtained. The

Patented Apr. 1, 1919.

Application filed. Qetober 7, 1914. Serial No; 885,504,

pig iron which I have used in carrying out this process contains .9 per cent. of-phosphorus. In every case, however, the pig 11011 contains a substantial percentage of silicon. \Vhen this pig iron is transferred directly to the basic-open-hearth and refined there, the high silicon content of theiron affects the percentage of phosphate which can be secured in the slag. A lime and ore slag is used. The lime combines with both the silicon and the phosphorus. Consequently, enough lime must he used to extract the silicon and also to extract the phosphorus. Silicon in the metal, therefore, means not only additional silica in the slag but additional lime in the slag; and in order to get out all or nearly all the phosphorus from the metal the slag has to be extremely voluminous under these conditions, and the percentage of phosphate is too low for a fertilizer.

I propose to first desiliconize the pig iron before extracting the phosphorus. The-desiliconizing may be performed in any usual or suitable way. duced to 1cm than one-half of one per centl, and preferably should be eliminated entirely. For this purpose an acid Bessemer converter may be used or the pig iron may be treated in any other intermediate vessel with a suitable slag; as, for example, in an acid open-hearth furnace or mixer with an acid slag of sand and ore. With an acid Bessemer converter practically all of the silicon contained can be removed from the pig iron without substantially reducing the phosphorus.

It is of great importance that all silicious slag resulting from this bessemerizing operation should be separated from the desiliconized metal, because should any silici'ous be carried with the molten metal into the refining or finishing furnace. the silica contained in that slag will displace phosphoric acid in the phosphoric slag which it is desired to obtain, the same as if the silica were obtained from the oxidation of silicon from the pig iron in the finishing furnace as is described above. This bessemerized product is then transferred to the openhearth or electric furnace and refined with a-basic slag which rapidly takes up phosphorus. When the slag contains the greater part ofthe phosphorus to be extracted this slag is withdrawn and second or finishing slag is added to complete the refining operhe silicon should be re- 'muchloweifpdrcentage of phosphates-than the first slag, and the first slag will be-correspondingly richer in phosphates than' if a single slag had been used for the removal of the entire quantity of phosphorus to be extracted. V

/ For convenient removal of the phosphoric slag it is preferable to use tilting furnaces having lips over which the slag can be run into cars or other receptacles and conveyed to suitable bins or grindingmachines for reducing it to the best size for use as a fertilizer.

At the completion of the refining operation in the open-hearth or electric furnace the metal may be poured into ladles and treated with manganese or other deoxidizin and finishing materials as usual and trans erred to'the molds. Preferably the final slag, containing too small a percentage of phosphates to be directly available as a fertilizer, is separated and transferred to the charge in the smelting furnace, with which it is mixed. This slag contains oxid of iron and lime, both of which are useful in mak ing up the charge in the smelting furnace.

. It hasalso the advantage in connection with this inj 'egntion of restoring to the charge the phosphorus which could not be economicall extracted in the refining operation. It f0 lows that the complete process will result in securing in the slag all the phosphorus in the ore (minus only the insignificant quan-' tities which remain inthe finished steel) and of extracting the same in a slag of the highest possible phosphate content; a residuum of phosphorus remaining continually in circulation in the plant.

Working the above process on a pig iron containing 0.9 per cent. phosphorus and 1.25 per cent. silicon, I first reduced this by an acid Bessemer operation to a metal containing one per cent. phosphorus and only traces of silicon. And from this metal I secured in the open-hearth operation a slag'containin 18.27 per cent. of phosphoric .acid '(P O, soluble in citric acid,- this being the usual commercial test of the solubility and value as a fertilizer.

In practice the first slag in the openhearth furnace cannot easily be entirely re moved, and it is not essential that it be entirely removed. One-half to two-thirds of this slag may be removed. More lime is added and this combining with theportion of the first slag remaining on the metal makes a final sla of lime and oxid similar to the first. ThlS final slag takes out the remaining percentage of phosphorus which has to be removed.

In'carrying out the process in the electric furnace, which is preferably of the Heroult are t e, certain changes have to be introduce owing to the neutral or deoxidizing has, therefore, be continued until the phds- .run through the plant wi out loss.

condition of'the atmosphere. The final slag should contain an addition of coke dust. This reduces the oxid so that the final slag takes out no phosphorus. The first slag.

phorus extraction is completed. Or the dephosphorizing operation may be carried on with two slags, one for-"roughin and one for finishing; after which the fina slag with coke dust is used. In this operation generall only the roughing sla will contain a su cient percentage of so uble phosphate to be valuable as a fertilizer, but the second or finishing dephosphorizing slag may be When usmg a pig iron containing only .2 per cent. to .3 per cent. of phosphorus a portion ofthe open hearth plant, say one quarter of the furnaces, may be used to' produce steel and a high phosphoric slag, while the slag from the remainder of the open hearth plant, say three-quarters of the furnaces, may be returned to the smelting furnaces to increase the phosphorus in the pig iron, which phosphorus is recovered in the open hearth furnaces used especially for producing high phosphoric slag.

Instead of usin the metal completely desiliconized in the essemer converter, I mayfurther modify the composition of this metal by recarburizing it by the addition of 1 a small percentage of ig iron or other carso as to avoid skulling in the ladle. Ithas the glrther advantage that the metal broug t to the open hearth is practically steel with a high ercentage of phosphorus so that the openearth furnace has nothing to do but to extract the phosphorus.

The resulting steel will be of the highest 115. quality, equivalent to that which is obtained in basic open-hearth furnaces working on a high percentage of steel scrap; the product produced by mixing the Bessemer metal and the pig iron being practically as good as scra T ough I have, described with great particularity of detail certain specific embodiments of my invention, yet 1t -is not to be understood thereffiom'that-the invention is 12:5

limited to the specific embodiments described. Various n rodifications may be made by those skilleddn' the art without departingfrom the invention as defined in the following claims;

atent No. 1 014,425 of January 9, i

What I claim is p 1. The process of prmlucing steel and a slag rich in phosphates which consists in desiliconizing pig iron without substantially' reducing the percentage of phosphorus and refining the desiliconized metal with a basic slag. and removing the slag before the end of the refining ope 'ation and when it contains the greater part of the phosphorus to be extracted.

2. The process of producing steel and a. slag rich in phosphates which consists in smelting the ore and forming pig iron. desiliconizing such iron to reduce the silicon content without substantially reducing the percentage of phosphorus. and refining the desilicomzed metal with a basic slag. removing the slag before the end of the refining operation and when it contains the greater part of the phosphorus to be extracted, adding slag-forming materials to complete. the refining operation and transferring the final slag to the charge in the smelting furnace.

3. The process of producing steel aml a slug rich in phosphates which consists in de siliconizing pi; iron without substantially reducing the percentage of phosphorus. thoroughly separating all silicious slag from the desiliconized metal. and refining the desiliconized metal with a basic slag. and removing the slag before the end of the refining operation and when it contains the greater part of the phosphorus to be extracted.

4. The process of producing steel and a 'slag rich in phosphates which consists in smelting the ore and forming pig iron. desiliconlzing such iron to reduce the silicon content. without substantially reducing the;

5. The process of producing steel and a slag rich in phosphates, which consists in desiliconizing pig iron without substantially reducing the percentage of phosphorus, recarburizing the desiliconized metal, refining it with a basic slag. and removing the slag before the end of the refiningoperation and when it contains the greater part of the phosphorus to be extracted.

(i. The process of producing steel and a slag rich in phosphates, which consists in hessemerizing pig iron to reduce the silicon content without substantially reducing the percentage of phosphorus. adding pig iron to the bessemerized metal to substantially convert it into steel with a high phosphorus content. refining it with a basic slag. and removing the slag beforethe end of the refining operation and when it contains the greater part of the phosphorus to be extracted.

7. The process of producing steel and a slag rich in phosphates which consists in smelting ore and forming pig iron, dcsiliconizing the pig iron without substantially reducing the percentage of phosphorus, refining the desiliconized metal with a' basic slag. transferring a part of the slag so used to the charge in the smelting furnace and thus increasing the phosphorus content of the pig iron and ot' the slag in'snbsequent refining operations.

S. The process of producing steel and a slag rich in phosphates which consists in desilicouizing pig iron without substantially reducing the percentage of phosphorus. removing the resulting high silica slag and refining the desiliconized metal with a basic slag. and removing the slag before the end of the refining operation and when it contains the greater part of the phosphorus to be extracted.

Tn witness whereof, I have hereunto signed my name in the presence of two subscribing witnesses.

WILLIA'MQR. \VALKER.

\Vitnesses:

D. As'ruoNY USINA, LULU STUnnNvoLL. 

